1. Field of the Invention
The present invention relates to the bending of pipe. More particularly, it relates to the bending of submerged pipeline used for the transportation of oil and gas from offshore wells and production facilities.
2. Description of the Prior Art
The development of offshore oil fields in deep waters has necessitated the laying of lengthy pipelines in order to transport oil and gas from remotely located fields to more centrally located production facilities and storage terminals. A major problem frequently encountered in laying pipeline is the making of pipeline connections, especially the second end connection of the pipelines. If a pipeline is laid over great distances and in deep waters, it is almost impossible to precisely align the end of the pipeline with its desired point of termination point. In most instances, correction of the misalignment must be made in order to make the final pipeline connection.
One conventional approach for correcting misalignment is to add a spool piece between the end of the pipeline and the point of termination. Normally, the spool piece is a specially designed section of pipe which is accurately fabricated and cut so as to correct for any misalignment. After it is fabricated, the spool piece must be either welded or flange connected to the pipeline end. In shallow waters, joinder of the spool piece and pipeline can be accomplished with the assistance of divers. Beyond demonstrated diver capability depths of about 500 feet, the spool piece must either be remotely installed or the pipeline end must be retrieved for an above surface connection. Retrieval of the pipeline and above surface connection is a time consuming and extremely expensive technique. Other techniques such as remote installation using subsea manipular devices are still unproven and may not provide the reliable, repairable, leakfree connections which are required of an underwater pipeline bend.
Another, less conventional, approach is to bend the pipeline itself to correct for the misalignment. As the pipeline approaches its point of termination it is a relatively simple matter to compute the amount of bending necessary to terminate the pipeline end at the desired target. In most instances, the pipeline should be laid out so that it can be bent at approximately a right angle. Such a "right angle" termination automatically adjusts for errors in pipeline length and angular misalignment and permits the use of relatively simple connector tools to make up the final connections.
The major problem with pipeline bending is the difficulty encountered in accurately bending the pipe and bending it a sufficient distance without buckling or otherwise damaging the pipe. If the pipeline is lifted or suspended off the sea floor there is great difficulty in bending the pipe a sufficient amount since there are no restraining forces on the pipe to effect an adequate bending moment. On the other hand, if the pipe is rested on the sea floor, the inertial forces caused by the heavy pipeline laying on the pliant sea floor will be extremely high, making the pipeline difficult to move or bend gradually. However, once the frictional forces are overcome the pipeline is likely to move very rapidly, making accurate bending difficult to control and possibly causing the pipeline to buckle or deform.
There is, therefore, a need in the art for a reliable technique for accurately bending offshore pipeline so as to permit expedient and economical pipeline connections.